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IEEE 802.11ah is an emerging wireless LAN standard at sub-1-GHz license-exempt bands for cost-effective and range-extended communication. One of the most challenging issues that need to be overcome in relation to IEEE 802.11ah is to ensure that thousands of stations are able to associate efficiently to an access point. During network initialization...
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... We compare results with the traditional schemes considering both QoS and non-QoS traffic. The existing solutions optimise RAW size based on delay and energy consumption [33], reduce association delay [34], and control loop latency [10]. To the best of our knowledge, this work comes as the first for proposing a traffic classbased QoS with dynamic grouping in 802.11ah. ...
The recent IEEE 802.11ah amendment has proven to be suitable for supporting large-scale devices in Internet of Things (IoT). It is essential to provide a minimum level of Quality of Service (QoS) for critical applications such as industrial automation and healthcare. In this paper, we propose a QoS-aware Medium Access Control (MAC) layer solution to enhance network reliability and reduce critical traffic latency by an adaptive station grouping and a priority traffic scheduling scheme. First, a link layer representation of traffic categories as per the delay and reliability requirements is proposed. Second, a novel backoff size-based slot scheduling scheme for Restricted Access Window (RAW) is proposed to support QoS. Third, a grouping scheme is proposed to calculate the current traffic load and balance it among different RAW groups. Finally, a Markov-chain model is developed to study the throughput and latency behaviors of the traffic generated from the critical application. The proposed protocol shows significant delay improvement for priority traffic. The overall throughput performance improves up to 12.7% over the existing RAW grouping scheme.
... When communication to an AP is required, all STAs before the communication should initiate authentication/association setup with the AP, as indicated in Figure 5 [81]. An STA transmits an authentication request (AuthReq) and association request (AssocReq) to an AP, allowing the AP to discover the existence and capabilities of the STA [22,[82][83][84]. ...
... Their study revealed that the association procedure might take several minutes and argued that a new method is required to prevent collision between AuthReqs and traffic from already-associated STAs with AP. In addition, [81] demonstrated that the optimal group of STAs can result in minimum association time. However, for the link setup procedure, the assumptions presented in [81] are the constant probability of successful transmission and the AP intelligence of how many STAs will be asking for connections, which are unrealistic. ...
... In addition, [81] demonstrated that the optimal group of STAs can result in minimum association time. However, for the link setup procedure, the assumptions presented in [81] are the constant probability of successful transmission and the AP intelligence of how many STAs will be asking for connections, which are unrealistic. To effectively register STAs with an AP, the slotted-CSMA/CA with time division multiple access (TDMA) was proposed in [91]. ...
IEEE 802.11ah, known as Wi-Fi HaLow, is envisioned for long-range and low-power communication. It is sub-1 GHz technology designed for massive Internet of Things (IoT) and machine-to-machine devices. It aims to overcome the IoT challenges, such as providing connectivity to massive power-constrained devices distributed over a large geographical area. To accomplish this objective, IEEE 802.11ah introduces several unique physical and medium access control layer (MAC) features. In recent years, the MAC features of IEEE 802.11ah, including restricted access window, authentication (e.g., centralized and distributed) and association, relay and sectorization, target wake-up time, and traffic indication map, have been intensively investigated from various aspects to improve resource allocation and enhance the network performance in terms of device association time, throughput, delay, and energy consumption. This survey paper presents an in-depth assessment and analysis of these MAC features along with current solutions, their potentials, and key challenges, exposing how to use these novel features to meet the rigorous IoT standards.
... Since the 802.11ah standard was published in early 2017, enhancing the association process of the standard has been an active research area [33][34][35][36][37][38]. In this section, we will describe a few studies with published performance results [39][40][41][42]. ...
... Moreover, the assumptions they made in their study cannot be fulfilled easily in real IoT network environments. An analytical model that is able to calculate the best group size, which leads to minimum association, time was proposed in [41]. The authors obtained the best group size for every beacon interval. ...
... A summary of the main issues described by the schemes proposed in [39][40][41][42] is given in Table 3 below. A summary of comparative study reported in [7] between Zigbee 902.15.4 and 802.11ah is also presented in the table. ...
The 802.11ah standard is a new energy-efficient, wireless networking protocol which allows thousands of indoor and outdoor devices to be connected to the same access point. The Centralized Authentication Control (CAC) method, described in the standard, enables up to 8000 stations to be authenticated and associated with the same access point. A baseline implementation of the CAC method has been reported; however, it suffers from a few limitations. In this paper, an efficient methodology is proposed to minimize the CAC method’s association time. The proposed methodology allows the association of a large number of stations by predicting the size of the network followed by selecting the best step size that will enable fast association between the access point and the stations of the network. The methodology consists of three stages. The first stage provides a baseline implementation of the 802.11ah standard, while the second stage eliminates the effect of too large or too small step sizes. The third stage finds the optimal step size and step repeat for each network size and predicts network size based on queue size. The performance of the proposed methodology is evaluated and compared in terms of total association time, number of total trials and percentage of ineffective trials. The methodology outperforms the baseline implementation by achieving a 30% reduction in the total association time, 30% reduction in the total number of trials and 45% reduction in the total number of ineffective trials.
... P tr and P s are calculated as Eqn. (6)-(7) [20]. ...
... The expected average transmission time for a successfully delivered frame is computed [20] according to ...
To reduce network congestion, most fast association mechanisms in 802.11ah networks control the number of devices to associate each round based on the management queue size. However, the management queue can be manipulated easily by jamming attacks. In this paper, we discover such a vulnerability and analyze possible attack models, including continuous, periodic, and reactive jamming that can effectively exploit the vulnerability. To analyze the impact of jamming, we propose mathematical models to study the association process under jamming. Our finding is that jamming attacks can fail the association process and disable the connectivity of the network, which causes IoT applications such as security surveillance and critical event reporting unavailable. To defense the problem, we also propose methods to address different types of jamming attacks. Experiment results show that our proposals can defend against jamming attacks effectively. Index Terms-Fast association, 802.11ah, jamming attacks, defense.
... However, the authors do not ensure fairness among the RAW groups. A novel analytical model to estimate the association delay of IEEE 802.11ah protocol and determine optimum RAW group size from this analytical model ensuring minimum association delay compared to fixed group sizes was proposed in [5]. However, channel utilization, fairness, number of RAW groups and RAW slot duration are not addressed in this paper and grouping strategy is not clear. ...
... We compare results with the traditional schemes considering both QoS and non-QoS traffic. The existing solutions optimise RAW size based on delay and energy consumption [21], reduce association delay [19], and control loop latency [16]. To the best of our knowledge, this work comes as the first for proposing a traffic class-based QoS with dynamic grouping in 802.11ah. ...
The recent IEEE 802.11ah amendment has proven to be suitable for supporting large-scale devices in Internet of Things (IoT). It is essential to provide a minimum level of Quality of Service (QoS) for critical applications such as industrial automaton and healthcare. In this paper, we propose a QoSaware Medium Access Control (MAC) layer solution to enhance network reliability and reduce critical traffic latency by an adaptive station grouping and a priority traffic scheduling scheme. The proposed grouping scheme calculates the current traffic load and distributes among different RAW groups considering different requirements of the stations. The RAW scheduling scheme further provides priority slot access using a novel backoff scheme. Markov-chain model is developed to study the throughput and latency behaviours for the traffic generated from the critical application. The proposed protocol shows significant delay improvement for priority traffic. The overall throughput performance improves up to 12.7% over the existing RAW grouping scheme.
... Different association control mechanisms such as centralized and distributed [2] reduces overall delay using restrictionbased schemes. A grouping-based mechanism is proposed in [13], which further improves association delay. However, with the increasing relays and mobile stations, the current solutions fail to provide the same. ...
... This section presents some recent works that mitigated the drawbacks of the BEB algorithm in IEEE 802.11 standards, including IEEE 802.11ah [28][29][30][31][32][33][34][35][36]. As mentioned earlier, the IEEE 802.11ah ...
... MAC protocol of RAW reduces collisions in highly congested network scenarios by using EDCA and DCF access schemes to manage transmission attempts. In EDCA, two backoff-counter are used; the first backoff counter is used outside of the RAW slot, and the second one is used inside the slot [28]. Multiple stations can be assigned within a RAW slot, and they need to contend within their associated slot to have access to the shared channel. ...
The IEEE 802.11ah standard relies on the conventional distributed coordination function (DCF) as a backoff selection method. The DCF is utilized in the contention-based period of the newly introduced medium access control (MAC) mechanism, namely restricted access window (RAW). Despite various advantages of RAW, DCF still utilizes the legacy binary exponential backoff (BEB) algorithm, which suffers from a crucial disadvantage of being prone to high probability of collisions with high number of contending stations. To mitigate this issue, this paper investigates the possibility of replacing the existing exponential sequence (i.e., as in BEB) with a better pseudorandom sequence of integers. In particular, a new backoff algorithm, namely Pseudorandom Sequence Contention Algorithm (PRSCA) is proposed to update the CW size and minimize the collision probability. In addition, the proposed PRSCA incorporates a different approach of CW freezing mechanism and backoff stage reset process. An analytical model is derived for the proposed PRSCA and presented through a discrete 2-D Markov chain model. Performance evaluation demonstrates the efficiency of the proposed PRSCA in reducing collision probability and improving saturation throughput, network throughput, and access delay performance.
... In [10], [11] the authors consider that AuthReps/AReps are transmitted instantly after AuthReqs/AReqs. However, HaLow defines that these frames should be first acknowledged by the acknowledgment frames (Acks). ...
In Wi-Fi HaLow networks, sensors can transmit data only after the link set-up procedure (LSP). After a power outage or when a swarm of sensors appears in an Internet of Things network, all of them contend for the channel to set up links with the access point. For thousands of sensors the LSP can last for hours. However, it can be shortened with advanced LSP coordination algorithms. We show that the best standardcompatible solution found in the literature leaves a gap between the achievable link set-up time and the estimated lower bound. In this paper, we design and evaluate an adaptive solution to control the LSP that fills in this room for improvement and provides significant gains against the existing algorithms.
... Congestion is detected if the MQS is non-zero. In [14], Pranesh et al. presented yet another fast association method based on a Mathematical Model (MM) to find the optimal number of stations per round. ...
... This results in a large number of stations in each round in a large network, causing severe collisions, and it may also result in a few stations in every round in the case of a small network, causing low channel utilization. MM [14] theoretically studies the optimal number of stations per round. However, it is assumed that the authentication/association response does not follow the Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) backoff procedure and is immediately transmitted. ...
... For a considered slot, the probability for at least a transmission to be in the considered time slot P tr and the probability for a transmission to be successful P s can be calculated [14] as ...
Fast association aims to quickly associate a large number of stations with an access point in 802.11ah networks. Existing fast association mechanisms suffer from efficiency, fairness and robustness problems. In this paper, we propose the mechanism of Fast Association based on Speculating the nUmber of Stations (FASUS). FASUS adopts new methods for retransmission, thresholding and adaptive round selection, which greatly improve the association performance. Experiments show that FASUS is able to reduce the association time by 67.1% when compared with the Linear Increase Linear Decrease (LILD) method, which is one of the best-known mechanisms for 802.11ah networks. We formulate a mathematical model to analyze the association process and to determine the optimal number of stations per round. Furthermore, we propose two methods to address the inter-and intra-network interference in congested networks. To improve the robustness and fairness of the network, we propose new solutions to address two possible attacks: 1) the Denial-of-Service (DoS) attack, which can disable the whole network, and 2) the selfish node attack, which may unfairly allow the attackers to associate in a much faster way than normal stations.
